The temporal change of each of these characteristic traits follows the direction of increased benefit for success (i.e. growth) of its associated population (Appendix equation ); this concept had been derived for genetic traits in the works of [1]}, and was recently more stringently formulated by Metz and colleagues [2]}, [3]} as adaptive dynamics (AD). In AD, the population averaged value of a trait changes at a rate which is proportional to the gradient of the fitness function evaluated at the mean trait value. The AD approach was extended to functional traits of ecological communities [4]}, [5]}, and was first applied to cultural traits of human communities by [6]}.
